The present invention relates to the copying of originals using a photoelectrophoretic color process. A first and a second electrode web are transported from respective supply units to respective take-up units along a predetermined path. At least one of the electrode webs is transparent. During operation, one of the electrode webs continuously receives a coating of toner suspension at a coating station. Downstream of the coating station, the two electrode webs are combined to form a sandwiched film pack, between the constituent electrode webs of which the toner-suspension layer is confined. This film pack is exposed at an exposure station, and a toner image is photoelectrophoretically formed within the film pack. The toner image is then transferred onto a web of copy material, i.e., onto the material on which the final copy is to be formed.
With one known arrangement of this type, the electrode web material is continuously (non-intermittently) transported through the apparatus. It is exposed at an exposure station located in the vicinity of two guide rollers operative for combining the two electrode webs into the aforementioned sandwiched film pack. To this end, one of the two guide rollers is made of transparent material. The exposure per se is accomplished utilizing a deflecting mirror mounted on the structure of the apparatus but located within the transparent guide roller. The deflecting mirror deflects exposure radiation through the transparent material of the transparent one of the guide rollers onto the portion of the sandwiched film pack which is located between the two guide rollers. Downstream of these two guide rollers, the two electrode webs are pulled apart from one another, so that the toner image formed on one of the two electrode webs can be transferred to the final copy material.
Due to the curvature of the guide rollers, the part of the film pack therebetween actually exposed at any given moment is a very narrow transverse strip extending parallel to the guide roller axes. Accordingly, the system becomes of the type wherein successive transverse strip-shaped zones of the original are scanned, and successive transverse strip-shaped zones of the intermediate toner image are formed successively, i.e., in synchronism with the scanning of the original.
This involves many disadvantages, some of them specific to the fact that a photoelectrophoretic color process is involved. The relative movements involved in scanning the original and in transporting the film pack through the exposure station must be synchronized, involving cost for accurate synchronizing means. Furthermore, if the originals to be copied are for example film negatives, expensive equipment becomes necessary for regulation of image color and density; because the total exposure time for each successive transverse strip-shaped zone of the film pack is quite short, it is necessary to measure and evaluate each transverse strip of the original with respect to color and density prior to exposing the corresponding strip-shaped zone of the film pack, to assure that the exposure conditions are properly varied if for example an extreme of color or density is to be produced during the short-lasting exposure of one strip-shaped zone.
One reason for resorting to the inconvenience and complexity of a strip-by-strip exposure technique relates to the application of the toner-suspension layer to one of the electrode webs of the film pack. It is important that the toner-suspension coating be applied to the electrode web in question with perfect uniformity, to assure that the thickness of the applied layer be perfectly constant. As a practical matter, to ensure that this occurs, it is generally considered necessary that the electrode web receiving the toner layer be moved past the toner applicator at very constant speed and continuously (non-intermittently). For this reason non-intermittent transport of the web receiving the toner-suspension coating tends to dictate that the entire system operate non-intermittently, resulting in the type of strip-by-strip exposure technique in question.
Aside from the already mentioned synchronization and exposure-control problems inherent in such strip-by-strip exposure methods, there is also the disadvantage that the continuous (completely non-intermittent) transport of electrode web material stands in the way of optimal utilization of web material. For example, as the original just copied is moved out from the copying station and the next original moved in, the web material transported during this time interval will in general be wasted. The shorter the required exposure time (i.e., the higher the transport speed of the web material) relative to the time required for the changeover from one original to the next, the greater becomes the waste of electrode web material and toner suspension.